Process for internally oxidationhardening alloys, and alloys and structures made therefrom



y 5, 1965 c. D. COXE ETAL 3,184,835

PROCESS FOR INTERNALLY OXIDATION-HARDENING ALLOYS, AND v ALLOYS AND STRUCTURES MADE THEREFROM Filed Oct.- 2, 1961 2 Sheets-Sheet l FIG.3

INVENTOR AllChaglelaI DD. lC(loxe en 0 one ,,1;

BY 721M amqmfn wm/ ATTORNEYS y 5, 1965 c D COXE ETAL 3, ,835

PROCESS FOR INTERNAILLY OXIDATION-HARDENING ALLOYS, AND

ALLOYS AND STRUCTURES MADE THEREFROM Filed 001;- 2, 1951 2 Sheets-Sheet 2 FIGS FIG? INVENTORS. CHARLES D. COXE ALLEN S. MCDONALD, JR.

mgwha W 1 TORNEY United States Patent PRGCESS FQR INTERNALLY @XEATION- HARDENENG ALLOYS, AND ALLQYS AND STRUCTURES MADE THEREFRGM Charles D. Coxe and Allen S. Mcllonaid, 3n, Fairheid, @onrn, assignors to Handy 8: Harman, New York, N.Y., a corporation of New York Filed Oct. 2, 1961, Ser. No. 145,528 6 Claims. (Cl. 20-1325) This application is a continuation-in-part of my application Serial No. 749,502 filed July 19, 1959, now abancloned.

The invention relates to internally oxidation-hardened polycrystalline alloys which are nonbrittle and have improved strength without size limitations, to a process for producing such alloys and to structures made therefrom.

It is known that increased strength and hardness may be imparted to solid solution alloys comprising solvent metals having relatively low heats of oxide formation with solute metals having relatively high heats of oxide formation, by heating said alloys in a medium that is oxidizing to the solute metals, but is relatively nonoxidizing to the solvent metals. Hardening is thus obtained by internal oxidation of the solute metal, i.e., by the precipitation of very small refractory oxide particles of the solute metal in the matrix of solvent metal. Examples of alloys which heretofore have been hardened by internal oxidation are:

TABLE I Solvent metal Solute metal Percent of Atom percent solute by wt. of solute Magnesium 0.075 to 0.36 35 to 1.6

Aluminum 0.085 to 0.40 35 to 1.6

Beryllium 0.05 to 0.23 35 to 1.6 Do Alum um 0.15 to 0.69 35 to 1.6

Smaller or larger amounts of magnesium and aluminum as solute in silver as solvent metal, or beryllium and aluminum as solute metal in copper as solvent metal may be used, and the resulting alloys after the solute metal has been internally oxidized will exhibit a hardness greater than that of the solvent metal alone. However, if the solute metal addition is less than the lower limits indicated in Table I the resulting alloys after internal oxidation will not have adequately increased strength, and if the solute metal additions are greater than the upper limits indicated in Table I, the resulting alloys after internal oxidation may be unsuitable, particularly for the products of this invention, in that they cannot be cold-worked by normal commercial practices without likelihood of frequent fracturing. In general, it may be said that from 0.35 to 1.6 atom percent of magnesium or aluminum in silver, and beryllium or aluminum in copper covers the most effective range. This range i critical in that below the lower limits inadequate results are obtained, while above the upper limits certain undesirable properties develop.

The essential requirements are that the solvent metal be a ductile metal capable of diffusing oxygen at elevated temperatures below its melting point without being itself converted to oxide, that the solute metal have a heat of oxide formation substantially higher than that of the solvent metal, and that the proportion of solute metal be large enough to be effective, but not so large as to cause formation of continuous oxide subscales or films that would inhibit further inward diilusion of oxygen or lead to products of low ductility.

The increase in strength that may be obtained by internal oxidation hardening of alloys such as those referred to above is considerably greater than can be obtained by the simple admixture of oxide powder with metal powder. However, in accordance with prior procedures, the internally oxidized solute metal has intergranular brittleness due, presumably, to a relatively high concentration of oxide in the grain boundaries of the alloy. Another disadvantage of the internally oxidized alloys as heretofore prepared, is that their use is confined to relatively light sections of strip and wire because the time required for oxidation increases as the square of the diameter or thickness.

Since the degree of hardening obtained by internal oxidation is dependent upon the rate of oxygen penetration into the alloy, as well as on the content of oxidizable solute metal, and since the rate of oxidation decreases as distance from the surface of the piece increases, hardness of a piece of internally oxidation-hardened alloy at its center is less than the hardness of the piece at the outer portions thereof. The thicker the piece, the more pronounced is this eifect. Also, the time required for oxidation hardening increases fourfold when the thickness is double. Thus, it becomes apparent that with the processes Thickness: Time 0.010" min. 22 0.020" hrs. 1.5 0.040" hrs. 6 0.080" hrs. 24 0.160" days 4 0.320" do 16 The time for complete internal oxidation of the solute metal can be decreased somewhat by substituting pure oxygen for air, or increased by lowering the oxygen activity of the medium employed. Thus, it is apparent that the degree of hardening depends not only on the content of the solute metal, but also on the rate at which the solute metal is internally oxidized, and this in turn depends upon the physical size of the pieces being treated, the temperature, and the oxygen content, or potential of the oxidizing medium. For these reasons the optimum solute metal content cannot be categorically defined for all conditions of oxidation time, temperature, oxygen content or potential of the oxidizing medium, and the thickness of the pieces being oxidized.

The internally oxidized alloys heretofore known have been subject to a type of failure which has been termed delayed brittle fracture. This may be demonstrated by the following test, described in connection with FIGS. 1 to 3, of the accompanying drawings, in which:

FIG. 1 is an edge View of an alloy strip resulting from the hardening operation of the type described above;

Feb. 2 is an edge view of a metal frame holding the alloy strip of FIG. I in curved position; and

FIG. 3 is a view similar to FIG. 2, showing the failure of the alloy strip.

In carrying out the test, the fiat alloy strip or sheet 1, say about 4" long and 0.50" wide and 0.020" thick, is bent into a bow shape so as to produce stress near the yield point in the outer fibers of the strip, and then is placed into the rigid frame 2 which holds the strip in this bent shape, as shown in FIG. 2. Several of these identical assemblies of the bowed strip, each restrained at its ends, were held at room temperature for about 20 hours.

heated at 1000 F. for 6 hours.

produced by the practices used heretofore will crack, as

Those strips which did not fracture are heated at 500 F. for 6 hours, and those surviving this second stage are In this test, the alloys shown in FIG-3. Conventional internally oxidationhardened alloy strip, where the strength exceeds 65,000

p.s.i., will often fail at room temperature, and almost invariably at 500 or 1000 F. Material which passes this test hereafter is referred to as being free from delayed brittle fracture.

It has now been found that the shortcomings of internally oxidation-hardneed alloys prepared by the heretocal admixtures of oxide powders and metal powders.

Moreover, the internally oxidation-hardened alloys prepared in accordance with the present process do not lose hardness when subjected to brazing temperatures. Thus,

oxidation-hardened-alloys made in accordance with the present invention can be used for making parts to be assembled by brazing, with the assembled and brazed parts a retaining their initial hardness.

Table I shows the ranges of the most effective amounts of a luminum,1and magnesium in silver, and aluminum, and beryllium in copper for achieving after internal oxidation alloys which have both high strength and sufficient ductility to permit working in accordance with this invention. Other combinations of solute metals and solvent metals are possible, such as, (a) the addition of more than one solute metal to one solvent metal, or (b) the addition of one or more solute metals to an alloy or mixture of solvent metals. In all such cases optimum combinations of strength and ductility are obtained when the total atom fraction of solute metal lies within the range of from 0.35 to 1.6 percent.

Inaccordance with the present invention, alloys of the type included in Table I are first powdered or comminuted by any of several conventional means, such as by atomizing the molten alloy, or otherwise producing powder by filing, grinding, or machining a solid piece of the alloy to" produce chips, turnings or swarf. Small, spherical sho of the alloy may be used, or larger shot may be flattened in a rolling mill or by hammering to produce the particulate material required. The essential feature of this step is to produce particles or pieces of an appropriate solvent metal containing in solid solution an internally oxidizable solute metal, these particles having a relatively high ratio of surface to mass. Machine chips about 0.010" to 0.020" thick are of a convenient and economi cal size. Powders ranging in size from 325 mesh to 0.050" diameter may be used. Generally, it is desirable for the smallest dimension to be less than about 0.060

so that the time for complete oxidation of the solute metal is not unduly extended, and the centers of the particles be not markedly less hardened than the surface portions.

These solid solution particles are then heated in a suitable oxidizing environment to internally oxidation-harden them by causing the solute metal to oxidize without appreciable oxidation of the solvent metal.

In the case where silver is the solvent metal, air provides a suitable oxidizing environment. In other cases, such an environment maybe obtained, in practice, by several means, such as, (a) exposing the alloy to be internally oxidized to a gaseous atmosphere in which the partial pressure of oxygenvis controlled by metering, (b) maintaining the alloy'to be internally oxidized within a closed system together with a compound containing oxygen which will furnish a suitable partial pressure of oxygen, (c) maintaining the alloy to be internally oxidized within a closed system together with the stoichiometric quantity of oxygen gas necessary to completely oxidize the formation of the hard dense pellets referred to above the solute metal, (d) maintaining the alloy to be inter nally oxidized in a closed system together with an oxygencuprous oxide is in contact with the alloy to be internally oxidized, the internal oxidation will proceed at maximum rate. If, however, the cuprous oxide is separated by an inert gas from the alloy to be internally oxidized, the ratecontrolling process is found to be the transport rate of the oxygen bearing species from the cuprous oxide through the inert gaseous phase to the surface of the alloy to be internally oxidized. Thus it is desirable for maximum internal oxidation rate, to pack the material to be oxi-q dized in cuprous oxide powder of a particle size smaller than the particle size of the alloy to be oxidized and later separate'the mixture by screening, as it is undesirable to leave a large excess of cuprous oxide in the alloy particles to be coaiesced. However, if this is attempted and the internal oxidation is carried out at temperatures of 1700 F. and above, which temperatures are desirable for maximum oxidation rate, it is found that the cuprous oxide sinters to an extent that makes screening of the cuprous oxide from the mixture difficult or impossible. If the mixture of alloy. and sintered cuprous oxide is milled, most of the sintered cuprous oxide is reduced to a powder which can be separated by screening. However, there always remains afraction of cuprous oxide in the form of hard dense pellets which milling will not reduce to. powder less than 150 mesh. A unique way to overcome these practical difficulties and a technique which prevents is to use as oxidizing medium a mixture containing, for example, 50% cuprous oxide powder by volume, and 50% aluminum oxide powder, by volume, which mixture previously has been sintered in an inert atmosphere at a temperature above 1600 F. and then tumbled to break up agglomerations and screened through 100 mesh. If the alloy to be oxidized is packedin such a mixture and internally oxidized at 1750 F. for 6 hours, the oxide mix-,

ture readily may be separated from the internally-oxidized alloy by screening. The chips from this step may be used directly if the chip surface is smooth enough for easy mechanical separation of adhering cuprous oxide powder; otherwise the chips may be pickled for external oxide removal, or heated in a reducing atmosphere at a lower temperature (about 750 to 1000" F.) to reduce the cuprousoxide adhering to the copper. The particular mixture of 50%, by volume, of aluminum oxide, and 50%, by volume, of cuprous oxide, represent but one example of the process. In general, any refractory oxide suchas beryllia, silica or magnesia will serve to inhibit the sintering of the cuprous oxide and may be used. Mixtures of from 25%, by volume, to 75%, by volume, of cuprous oxide, with the balance refractory oxide have been used successfully. I I

The internally oxidation-hardened particles then are coalesced into a single larger piece at elevated temperatures, but below the melting point of the solvent metal, and at high pressure to cause at concomitant plastic deformation of the hardened particles equal to at least 75% reduction in cross-sectional area. This may be done by hot extrusion, or by hot pressing. In either case, the coalesced piece subsequently may be subjected to hot or cold rolling, drawing or swaging. By this means it is possible to produce internally oxidation-hardened alloys of optimum hardness in thicknesses impossible to produce by heretofore known means. The properties of the resultant oxidation-hardened structures are unique, and they may be used in applications for which internally oxidationhardened alloys heretofore available were not suitable.

Example I An alloy, of 0.3% by weight, of magnesium, with the balance silver, was atomized from the melt to produce This powder was formed into layers the use of as much as 0.40% of magnesium as solute metal is unsatisfactory.

Material containing 0.30% magnesium or less could be easily cold worked after extrusion.

325 mesh powder. In all of the examples, the inverted extrusion process thick and oxidized in air enriched with oxygen at was used i.e., the die being pushed into the extrusion con- 13 50 F. for one hour, at which time all of the magnesium miner, Thi method favor lowe tr i pressure, in the alloy was oxidized. The oxidized powder was The properties of extruded material containing 0.30% placed in a silver can 35" in diameter and of 0.1" wall magnesium as described in this example and the properties thickness and heated until the powder reached 1400" F. of 0.30% magnesium material as described in Example The powder was then placed in an extrusion press having III were, on the average, the same. Typical values are an 0.625" diameter die, and pressed and coalesced at 600 listed in the following table. tons. The powder failed to extrude through the die, the bulk of it escaping between the extrusion container and ram, leaving an 0.135" thick tablet of coherent, coalesced, 15 t Reductiotnin Utltirnittc Elonggtion hot ressed metal in the container. This material had er M55590 6115129 111 a ha idness of Rockwell 1385. The material was cold (percent) (percent) rolled to 0.071". The ultimate tensile strength at 0.071 10 62 000 17 was 84,000 p.s.i. The material was then annealed at 20 67:000 11 1000 F. for one hour and cold rolled to 0.030". The 2g 88g 9 following properties were determined: 85 851000 5 96 80,000 4 Yield Ultimate 1 AS extruded- (nii iiir il la) it??? sii ii g t h Samples of 0.125" diameter cold drawn rod containing 0.30% magnesium as described in this example and samples of 0.125" diameter cold drawn rod as described in 2 5 253 ,-a ga- 000 000 Example III were annealed in air for one hour at tempera- 1 hr 85 63,000 64,000 tures in the range from 600 F. to 1700 F. and tensile f at 1 f m 76 57 000 59 000 tested. Average values for both materials were the same.

"""""""" Typical values are listed below.

The 0.030" strip thus produced was not susceptible to A t t o F t g delayed brittle fracture when tested by the method deg g empera 61151 6 Strengt scribed above.

Example I was repeated except that the extrusion 1200 84,000 temperature was raised to 1500 F. An extruded rod was 1400 81,000 obtained from the powder thus coalesced having the fol- 1600 70,000 lowing properties: 1700 51,000

Yield Ultimate Hardness strength tensile (Rockwell B) (p.s.i.) strength Rod, as extruded 72 58, 800 63, 000 Annealed 1,000 I., 1 hr 72 56,000 63,000 Annealed 1,400" F., 1 hr 62 56, 100 59, 000 Annealed 1,600 F., 1 hr 56 48, 800 900 Example 111 Sheet metal 0.02" thick of the composition of 99.5% silver, 0.3% magnesium, and 0.2% nickel (the nickel added as a grain refiner, not as a hardener) was chopped into pieces approximately 0.25 square and substituted for the powder in Example II. On extrusion, at 1500 F. a coalesced rod was obtained. Its properties were the same as those set forth below in the tabulation of Example IV. In each of Examples II and III the extrusion ratios were 21 to 1.

Example I V Samples of 0.125 diameter cold drawn rod containing 0.30% magnesium, balance silver, as described in this example and samples of cold drawn rod as described in Example III, both as drawn and annealed at 1200 F., were tested for delayed brittle fractures, and were found free of this condition. A rod was used in place of the strip shown in FIGS. 1 to 3.

Samples of 0.100" diameter cold drawn rod containing 0.30% magnesium, with the balance silver, as described in this example, and samples of 0.100" diameter cold drawn rod as described in Example III, were used to determine short time hot tensile strength, and electrical conductivity. Typical results from these tests are listed below. The table also includes for comparison typical values for conventional internally oxidized (at finished size) wrought material of the same composition. The superior ductility at elevated temperature of the material of this invention as compared with conventional internally oxidized product is noteworthy.

SEORI TIME I-IOT TENSILE STRENGTH DATA *Solid solution oxidized at finished gauge.

CONDUCTIVITY DATA (IN PERCENT OF INTERNATIONAL ANNEALED COPPER STANDARD) Conventional New product product Test temp.

The following Vickers Hardness values (200 gm. load) were determined on a section of 0.187% diameter extruded and cold drawn rod of this example. These results establish the uniformity of hardness across heavy sections. It is well known that in conventional internally oxidized wrought materials the hardness decreases with increasing distance from the surface,

truded rods for various beryllium contents are listed below.

Ultimate Reduction in Beryllium content tensile Elongation area at fracture (wt. percent) sgrenggh in 2 (percent) (percent) Example VI Extruded rod of .750" diameter containing 0.10% beryllium with the balance copper, was drawn with and without anneals between draws. The results of tensile tests at various diameters are listed below. 7

Distance from surface: VHN (200 gm. load) QZ 1 8 0004 118 0010 122 0 046 117 0.093 (center) 122 It is apparent that a marked and unexpected improvement is obtained in the product of our invention as compared with the internally oxidized silver alloys heretofore known. This is shown in (1) uniform hardness across large sections, (2) complete hardening, (3) absence of delayed brittle fracture, (4) higher hot strength, and (5) higher electrical conductivity.

Other work (not reported herein in detail) has shown that for silver-base alloys, magnesium is superior to aluminum as an oxidation hardener, and that within the range of effective compositions shown in Table I the optirrium magnesium content is 0.20% to 0.35%, by weight, with or without about 0.2% nickel, with the balance silver.

Example V Using procedures similar to those described under Example IV, extrusion billets were prepared from alloys containing from 0.05% to 0.20% beryllium, with the balance.

copper. Either chopped sheet (about .020" thick), or

- milling machine chips (about .020 thick), were used Example VII The following average value of Vickers Hardness numbers (200 gm. load) was determined on a section of 0.287 diameter extruded and cold drawn rod of 0.10 beryllium (as beryllium oxide), with the balance copper.

Distance from surface: VI-IN (200 gm. load) 0.070" 132 0.143" (center) 130 Average values of Vickers Hardness numbers (200 gm. load) determined on a section of 0.016 diameter conventional internally oxidized wrought material of the same chemical composition were as follows:

Distance from surface: VHN (200 gm. load) 0.004" 0.006 132 0.008" (center) e 121 These results demonstrate the uniformity of hardness obtainable across large sections of the material of this invention.

All of the materials discussed in the above examples were free of delayed brittle fracture when tested as described above.

The properties of the copper-0.10% beryllium material of this invention are compared below with the properties of a conventional commercial alloy of 0.12% zirconium, with the balance copper. The comparison is made with respect to this latter alloy because it has the highest strength of any commercial copper alloy with electrical conductivity over 80%. The following data, determined on 0.100 diameter rods of copper-0.10% beryllium cold drawn from an extruded diameter of 0.750, and on 0.100" diameter rods of commercial heat treated copper- 0.12 zirconium alloy compare the room temperature properties of the two materials.

The following data determined on specimens as de scribed in the previous paragraph compare the short time hot tensile strengths of the oxidation-hardened alloys of this invention and the copper-zirconium alloy of commerce.

Ultimate tensile Elongation in 2 strength (percent) Test temp.

Oil-0.10 Cid-0.12 Cu-0.10 Gil-0.12

Be Zr Be Zr Room temp 91, 000 64, 000 6 400 F-- 77,000 4 Using specimens as described above it was further determined that the ultimate tensile strength of the copper- 0.l2 zirconium alloy dropped from 64,000 psi. to 43,000 p.s.i. on annealing for ten minutes at 1200 F., and dropped from 64,000 psi. to 37,000 p.s.i. on annealing for ten minutes at 1500 F., whereas the ultimate tensile strength of copper-0.10 beryllium originally at 90,000 p.s.i. was at the high level of 77,000 psi. after annealing for 120 minutes at 1500 F. These figures demonstrate that the copper-0.10 beryllium alloy of this invention can be subjected to the temperatures involved in all common brazing operations and still maintain a high strength level whereas the commercial copper-0.12 zirconium alloy cannot.

Using specimens as described above the electrical conductivity of the copper-0.10 beryllium alloy was determined to be 85% IACS and that the copper-x12 zirconium 90% IACS.

The extruded rods of the preceding examples were free of delayed brittleness.

Thus, the present invention provides a process for producing internally oxidation-hardened alloys having a new combination of high strength at room temperatures and at temperatures up to 1500 F, and high electrical conductivity not equaled by any internally oxidation-hardened copper alloys heretofore known.

Within the range of eifective compositions shown in Table I, we find beryllium is superior to aluminum as an oxidation hardener, and for the purposes of this invention, from 0.05% to 0.15%, by weight, is the optimum beryllium content; while 85% IACS is a typical value for the conductivity of the 0.1% beryllium alloy of this invention, values between 80% and 90% may be obtained depending on composition and incidental impurities.

The internally oxidation-hardened polycrystalline alloys of the invention are particularly useful in articles where a combination of high electrical conductivity, high strength at elevated temperatures, resistance to softening at brazing temperatures, and ability to be fabricated in heavy sections are desirable. FIGS. 4 to 8 of the ac companying drawings show representative articles in which the new internally oxidation-hardened alloys of the invention are particularly useful. In these figures,

FIG. 4 is a perspective view of a solid spot welding electrode,

FIG. 5 is a perspective view of a brazed spot welding electrode,

FIGS. 6 and 7 are side elevational and central crosssectional views, respectively, of a brazed wheel electrode, and

FIG. 8 is a perspective view of a contractor arm.

Internally oxidation-hardened alloys described in Example VI, but in the form of a .25 diameter rod 2" long, were fabricated into a spot welding electrode 5 (FIG. 4), one end of which is machined to form a truncated conical section 6 terminating in a planar working surface 7. Electrodes of the form shown in this figure were used for mak ing resistant welds in steel sheets, and the attrition of the electrodes was compared with commercially available heat-treated chromium-copper and cadmium-copper electrodes. In a series of 200 high current wells in carbon steel sheet, the heat-treated chromium-copper and the beryllium-copper electrodes mushroome-d to about the same extent. The wear on the oxidation-hardened beryllium-copper electrodes was slightly less than the wear on the chromium-copper electrodes. The two were judged to be about equal, and both somewhat better than the conventional softer cadmium-copper electrodes. The chromium-copper electrodes were annealed at 1300" F. to simulate a brazing operation and then tested. They bulged badly so that their useful life was reduced to to /5 that of the unannealed electrodes. The internally oxidation-hardened beryllium-copper alloy electrodes of this invention were unaffected by the 1300 F. annealing temperature.

In this application, it will be noted that had the electodes made from commercially available, heat-treated, chromium-copper and beryllium-copper electrodes, been machined from conventionally internally oxidation-hardened stock, the working area at the planar face of the electrode, being at the center of the truncated conical portion, would have been in the softer part of the electrode. However, with electrodes made from the internally oxidation-hardened alloys of this. invention, the center of the rod is as hard as its surface portions. In a conventional, internally oxidation-hardened rod 0.25 in diameter, the hardness decreases from VHN at the surface to 114 VHN at the center, whereas in the coalesced product of this invention, the hardness was substantially uniform at 130 VHN across the entire section.

It is also possible to make electrode tips of the internally oxidation-hardened alloy of this invention for attachment to electrode holders by brazing as in FIG. 5. In this figure, one end of an electrode holder 10 has a frusto-conical section or tip 11 formed of the internally oxidation-hardened polycrystalline alloys of this inven tion secured to it by a brazed joint 12. As in FIG. 4, the frusto-conical section terminates in a planar working surface 14. The brazing temperature necessary for forming the brazed joint 12 will not destroy the hardness of the tip 11 as it would in tips made of the chromium-copper and cadmiurn-copper alloys usually used, which are not internally oxidation-hardened. Such alloys usually con tain 0.8% chromium and 99.2% copper, and 1% cadmium and 99% copper, respectively.

For electrode wheels for seam welding, a rod of an internally oxidation-hardened alloy of this invention may be bent around the periphery of a copper or copper alloy wheel and be brazed in place to provide a firmly attached tire whose hardness is not destroyed by the brazing heat. Such a wheel is illustrated in FIGS. 6 and 7. In these figures, a wheel 20, of copper or copper alloy, has a tire 21 of the internally oxidation-hardened alloy of the invention secured to its periphery by brazed joint 22. The tire 21, in radial cross section, tapers outwardly to aperipheralplanar working surface 23. If tires such 7 'as the tire 21 are made from a heat-treated chromiumcopper alloy or'a similar work-hardened cadmium-copper circuit breakers, switch gear and the like, it is desirable tov afiix the contact pieces to the arm by brazing, without softening, the arm. In use, ohmic heating raises the temperatureof the arm while it is under high stress. For this specific application the resistance to annealing makes possible lighter and stronger contacts that react faster because of their lowerinertia.

' In FIG. 8 there is-shown a contact arm comprising a body 30-rnade of the internally oxidation-hardened alloy of this invention. Contact buttons 31 and 32 are secured to each end of the arm by brazed joints 33 and 34. The contact'arm being made of the internally oxidation-hardened alloy of the invention is not softened by the brazing of the contact buttons thereto, nor will it be softened by the ohmic heating which results from the use of the arm.

In the applications discussed above, the internally oxidation-hardened alloys of this invention based on both silver and copper as the solvent metal are of unusual value. Such combinations of high electrical conductivity, high strength at elevated temperature, resistance to softening at brazing temperatures, ability to be fabricated in heavy sections, all combined in a single material makes the alloys of the invention unique. Such a desirable combination of properties has not been obtained in any single alloy hereto tore known.

'Weclaimz r =1. The coalesced product resulting from the extrusion of internally oxidation-hardened particles of a solid solution alloy, said product consisting essentially of copper as the solvent metal and at least one solute metal oxide of the group consisting of beryllium oxide and aluminum oxide the amount of said solute met-a1 oxide being based on from about 0.35 to 1.6 atomic per-cent of the solute metal, said alloy particles having been completely internally oxidized entirely by the preferential oxidation of the solute metal alone, said particles being thus substantially free ofcopper oxide and of in situ reduced copper oxide,

said coalesced product havingsubstantially uniform hardness across the entire section and being substantially free of softlareas due to in 'situ reduced copper oxide, a tensile strength in excess of 60,000 p.s.i., being free from delayed brittle fracture, being capable of retaining at least 90% of the as-extruded strength after annealing in a neutral gas at 1400 F. for 1 hr. and an electrical conductivity in e excess of IACS at room temperature.

I 2. The pr-oductof claim 1 wherein the solvent metal 7 is copper and the solute metal beryllium, and the beryllium is present in amount of from about 0.05% to 0.15 V

of internally oxidation-hardened particles of a solid solu- 7 tion alloy, said product consisting essentially of copper as the solvent metal and at least one solute metal oxide'of the group consisting of beryllium oxide and aluminum oxide the amount of said solute metal oxide being based on from about 0.35 to 1.6 atomic percent of the solute metal, said alloy particles having been completely internally oxidized entirely by the preferential oxidation of the solute meta-l alone, said coalesced product having substantially uniform hardness across the entire section and being substantially free of soft areas due to reduced copper ox ide, a tensile strength in excess of 60,000 psi, being free from delayed brittle fracture, being capable of retaining at least 90% of the as-extruded strength after annealing in a neutral gas at 1400 F. for 1 hr. and an electrical conductivity in excess of 70% IACS at room temperature.

References Cited by the Examiner UNITED STATES PATENTS 2,545,438 3/51 Stumback 29 -1825 2,785,974 3/57 Moore 206 2,823,988 2/58 Grant 29-182.5 2,894,319 7/59 Thomson 29l82.5 2,894,838 7/59 Gregory 29-4825 2,952,903 9/60 Washken 29182.5 3,026,200 3/62 Gregory 75- 206 3,085,876 4/63 Alexander et al 29182.5

FOREIGN PATENTS 654,962 7/51 Great Britain.

OTHER REFERENCES I Journal of Metals, March 1957, page 351.

CARL D. QUARFORTH, Primary Examiner. REUBEN EPSTEIN, OSCAR R. VERTIZ,Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,184,835 May 25, 1965 Charles D. Coxe et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 12, for "July 19, 1959" read July 18,

1959 column 3, line 12, for "oxidation-hardneed" read oxidationhardened column 9, last table, last column, insert 9 as the last entry to the column.

Signed and sealed this 5th day of October 1965.

(SEAL) Altest:

ERNEST W. SWIDER EDWARD J BRENNER Attesting Officer Commissioner of Patents 

1. THE COALESCED PRODUCT RESULTING FROM THE EXTRUSION OF INTERNALLY OXIDATION-HARDENED PARTICLES OF SAID SOLUTION ALLOY, SAID PRODUCT CONSISTING ESSENTIALLY OF COPPER AS THE SOLVENT METAL AND AT LEAST ONE SOLUTE METAL OXIDE OF THE GROUP CONSISTING OF BERYLLIUM OXIDE AND ALUMINUM OXIDE THE AMOUNT OF SAID SOLUTE METAL OXIDE BEING BASED ON FROM ABOUT 0.35 TO 1.6 ATOMIC PERCENT OF THE SOLUTE METAL, SAID ALLOY PARTICLES HAVING BEEN COMPLETELY INTERNALLY OXIDIZED ENTIRELY BY THE PREFERENTIAL OXIDATION OF THE SOLUTE METAL ALONE, SAID PARTICLES BEING THUS SUBSTANTIALLY FREE OF COPPER OXIDE AND OF IN SITU REDUCED COPPER OXIDE, SAID COALESCED PRODUCT HAVING SUBSTANTIALLY UNIFORM HARDNESS ACROSS THE ENTIRE SECTION AND BEING SUBSTANTIALLY FREE OF SOFT AREAS DUE TO IN SITU REDUCED COPPER OXIDE, A TENSILE STRENGTH IN EXCESS OF 60,000 P.S.I., BEING FREE FROM DELAYED BITTLE FRACTURE, BEING CAPABLE OF RETAINING AT LEAST 90% OF THE AS-EXTRUDED STRENGTH AFTER ANNEALING IN A NEUTRAL GAS AT 1400*F. FOR 1 HR. AND AN ELECTRICAL CONDUCTIVITY IN EXCESS OF 70% IACS AT ROOM TEMPERATURE. 